The invention relates to a method of correcting the position of an image to be printed on a printing material.
Usually printing machines are provided with forward stops and side stops which serve to position sheets to be printed in precise positions in the printing machine.
By way of example U.S. Pat. No. 5,297,789 shows details of a front stop (xe2x80x9clayxe2x80x9d) for a printing machine. A side stop is typically constructed along the same lines. U.S. Pat. No. 5,297,789 is incorporated into this application by reference.
By these means a defined position of the printed image on the sheet is attained. The forward and side stops are adjustable, so that correction of the image position is possible. To that end the distance to the edges and parallel orientation of the image with respect to a test sheet is visually determined or manually measured, and the side stops are adjusted manually or by means of a motor.
Another approach to the image position correction is attained by means of the register adjustment devices provided for adjusting the printing form on the cylinders. This solution is, however, only practical when a small adjusting range is sufficient.
It is also known to examine with examining or scanning devices the entire surface of a printed material inside or away from a printing machine. The measuring signals from the scanning devices are used to interact with the processes for controlling the inking of the image.
It is the object of the invention to provide a method for image position correction which results in an independent method for correcting image position.
This object is attained according to the inventive concept, thereby that during printing on a printing material, image signals are generated by means of an image pickup device placed in the travel path of the image, wherein the image signals are taken from at least one surface of the printed material. From these image signals measuring values are obtained, which relate to the distance and degree of parallelity of the printed image in relation to the printed material, so that an image position correction can be attained.
The invention is especially advantageous when applied to sheet printing machines equipped with adjustable front and side stops for correction of the image position. An embodiment of the invention relates to a printing machine having a steering or control device arranged for so-called first form and perfector printing, and which additionally has devices for adjusting the turning registers. In that manner it is possible to simultaneously correct the image position on both the front and back of the printing material.
With the foregoing and other objects in view there is provided a method for image position correction in printing on a printing material, wherein the printing material is traveling along a travel path through a printing machine by means of a transporting arrangement, and wherein a positioning device is provided for aligning the distances and parallelities of the printed image in relation to the edges of the printing material, the method which includes the steps of:
generating by means of at least one image pickup device disposed in the travel path of the printing material image signals from at least one surface of the printing material, wherein the image signals contain information pertaining to the distances and parallelity of the printed image in relation to the edges of the printed material;
transmitting the image signals to a steering- or control device; and
adjusting with the steering- or control device by means of the image signals applied to aforesaid positioning device the printed image so as to attain alignment of the image in relation to the distances from and parallelity with the edges of the printing material.
In accordance with another feature of the invention, there is provided a device for correcting image position on a printing material in a printing machine having a transporting arrangement for transporting the printing material through the printing machine, and a positioning device for aligning the distances and parallelity of the printed image in relation to the edges of the printing material, the device which includes an image pickup device for picking up image position signals relating to distance and alignment of the image in regard to the edges of the printing material; a steering- or control device for receiving the image position signals and computing adjustment data for the image position, and setting means for receiving the adjustment data and setting the image to an adjusted position.
In accordance with a concomitant feature of the invention there is provided a device according to the invention, which includes in the printing machine means for performing first form and perfector printing, said means having a turning register, and devices for adjusting the turning register connected with said steering- or control device to attain alignment with the printing material.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of correcting the position of an image to be printed on a printing material, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which: